This invention relates to a control of a rotary body, and is particulary concerned with a method of controlling the speed of rotation of the rotary body of a false-twister and apparatus thereof.
In a typical process of crimping synthetic fibre yarn, a rotatable body, which is a false-twister spindle, running at high speed, twists the yarn fed from supply bobbin and heated previously for the purpose. The twisted yarn is untwisted after leaving said rotary body and then taken up onto a bobbin. The main driving means for the rotary body may comprise an air turbine. The rotary body may be tubular and carry a rotor of an air turbine.
As the feeding and take up movement is driven independently of the twisting movement, without interrelation between each other, it is obvious that twist irregularity becomes unavoidable in case when the twisting speed is uneven, causing dyeing speck thereby. On the other hand, the speed up of the processing has become urgent in order to raise the efficiency of the production. It has become inevitable to keep the speed of the twisting spindle constant, as well as the speed of winding the yarn. Hereby, it is needed to devise means to control and stabilize the speed of rotation of the spindle, or means to make the speed resume its predetermined speed as quick as possible so far as the deviation of the speed lies within a certain tolerance.
Hitherto, the control of the rotating speed has been attempted by detecting the speed of the rotary body either continuously or intermittently, then comparing it with a reference value of speed, in case when the amount of deviation exceeds a fixed limit, the deviation value is simply fed back to the power control system of the drive. This method effects no control of speed when the deviation lies within the limited range fixed for such scheme of control.
Meanwhile, as the yarn is fed to the twister at a speed independent of the revolving speed of the twister, the gradual fluctuation of the latter may unavoidably cause twist irregularity of the yarn.
As such controlling procedure starts only after detecting the deviation of the rotary body from a fixed tolerance, it is natural that the starting of the controlling procedure can not occur before the fluctuation of speed has deviated out of the fixed tolerance to a certain amount, and the yarn is left running without remedy for the twist irregularity all the while.
Moreover, when the speed fluctuates over a minute duration of time and is restored automatically to its original speed after that, the recovery procedure will take the more time, the larger the amount of deviation, because of the moment of inertia of the rotating body, and because the transitional loading on the system will disturb the quick response of the system. This will be a cause of the twist irregularity appearing in spots or in a wave form distribution, lowering merchandise value thereof by the degradation.
So far as the speed of the rotary body is limited within a certain low value, the speed control may be accomplished by controlling the opening of the air supply valve to the turbine, or by changing the angle of injection of the air jet thereto, but, at present days, the revolving speed of the rotating body has reached 500,000 rpm, in some case more than 1,000,000 rpm. In such cases, the speed of the rotating body can hardly be controlled instantaneously through conventional means as by controlling the valve opening or by changing the direction of inclination of air jet to the turbine.
The output signal of a rotary body is, generally, picked up as one of electric quantities proportional to the speed of the body.
When the revolution of the controlled system restores the predetermined revolution through actuating the control system on the basis of the comparison of the speed signal of the rotary body with the standard or reference signal, a time lag is inevitable due to the feedback of the information. On the other hand, although the information is electrically transmitted to the control system, the time lag occurs while restoring the revolution of the controlled system within the predetermined tolerance because of the mechanical actuation in the actuator.
It means the inability of the system to restore the rotating speed to the fixed speed in instantaneous response to the fluctuation of the speed of the rotating body. Moreover, as the nature of the speed comparator in a control system, it starts sending the deviation signal or information to the speed regulator only when the amount of fluctuation deviated from the fixed limit of tolerance, a minute fluctuation of speed within the tolerance limit can not cause any compensating control of the system.